We have recently proposed certain functional similarities between the phenethylamine hallucinogens and the tryptamine type hallucinogens, including LSD. The objectives of this study are to prepare and pharmacologically evaluate substituted 1,2-dihydro-2-naphthylamines as rigid analogues intermediate in structure between the phenethylamines and LSD. Attempts will be made to develop quantitative structure activity relationships which define activity of the proposed compounds in terms of parameters such as partition coefficient and various quantum chemical indices. The long range goal is to gain a clearer understanding of the mechanism of action for hallucinogens, to identify the endogenous receptor(s) involved in the mechanism, and to define steric and electronic requirements for hallucinogenic activity. In view of the probable involvement of serotonin pathways in this action, we hope to define the requirements for interaction with these receptors.